Miniaturized 3 GHz cross-coupled planar microwave filters

Cross-coupled planar microwave filters were fabricated using YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// superconducting thin films deposited on both sides of a LaAlO/sub 3/ single crystal substrate by pulsed laser deposition. The hairpin resonator geometry allows one to miniaturize the 3-GHz filters by compacting the entire filter onto a substrate with dimensions 0.5 cm /spl times/ 1 cm. By adjusting the relative spacing among the resonators to establish adequate couplings, filters with very sharp rejection skirt and extremely small insertion loss in passband were obtained.